It is known that when the ignition timing of an internal combustion engine is retarded with respect to the top dead center on the compression stroke of pistons, combustion speed of an air-fuel mixture taking place in the combustion chambers is reduced. As a result, although the output of the engine is lowered, pollutants contained in the exhaust emission can be reduced. On the other hand, when the ignition timing is advanced, the pollutants contained in the exhaust emission are increased and the output of the engine is increased.
Accordingly, in addition to control of the ignition timing to an optimum timing (Minimum Advance for Best Torque) depending on the engine revolution and intake manifold vacuum of an engine, there has heretofore been conducted a change-over control of the ignition timing between ignition-advance region and ignition-retard region so as to purify the exhaust gas and to enhance the engine output.
In an internal combustion engine provided with an automatic transmission, however, such a serious disadvantage that the driveability of a vehicle is degraded or reduced is brought about when the engine is operated under such a condition that the ignition timing is in the vicinity of the boundary between the ignition advance region and the retard region.
It is therefore an object of the present invention to eliminate the above-mentioned disadvantage encountered by the conventional automatic transmission used in combination with an internal combustion engine.
Another object of the present invention is to provide means for controlling the drive range operation of an automatic transmission used in combination with an internal combustion engine whereby the shifting characteristic of the automatic transmission is changed depending upon whether the ignition timing of the engine is being advanced or retarded, so that the shifting operation by drive range control elements of the automatic transmission does not take place while the engine is operated under a boundary region where the ignition timing is frequently changed from the advance region to the retard region and vice versa.
In accordance with the present invention; there is provided an automatic transmission with torque converter adapted for use with an internal combustion engine of the type having an ignition control device in which the ignition timing of the engine is changed over from an advancing timing region to a retarding timing region or vice versa in compliance with change in the operating conditions of the engine, and means for automatic shifting from one drive range to another, said control means comprising:
shift valve means for controlling an occurence of automatic speed-shifting under the control of a throttle pressure and a governor pressure applied thereto, respectively;
governor valve means for supplying said shift valve means with said governor pressure generated in response to the speed of a vehicle on which the internal combustion engine is mounted;
throttle pressure supply valve means for supplying said shift valve means with said throttle pressure generated in accordance with an application thereto of a valve actuating input signal;
means for producing two different said input signals, each being a function of a negative pressure from an engine intake manifold; and;
means for selecting an application of one of said two different valve actuating input signals from said input signal producing means to said throttle pressure supply valve means in response to whether said ignition timing is in said advancing timing region or in retarding timing region.